This invention relates generally to heat exchanger apparatus in gas turbine engines, and more particularly to a variable geometry surface cooler in such gas turbine engines.
Aviation engines use heat transfer fluids, such as oil or fuel, to dissipate heat from engine components, such as engine bearings, electrical generators, and the like. Heat is typically rejected from the fluid to air by heat exchanger assemblies, such as fuel cooled oil coolers or air cooled surface oil coolers, to maintain oil temperatures at a desired ˜100° F.<T<300° F. In many instances, known heat exchanger assemblies, and more particularly surface coolers, typically found in aircraft engines are sized for ground idle (GI) conditions, when the temperature of the surrounding air is higher and the air speed is lower than during other phases of flight, such as found during inflight conditions. In addition, these known surface coolers are designed for use during top of climb conditions. Both ground idle conditions and top of climb conditions require a heat transfer area in the heat exchanger that is greater than during other phases of flight, such as found during inflight conditions. As such these known heat exchanger assemblies are designed for maximum heat exchange performance. For cruise conditions, such as during inflight, when the temperature of the surrounding air is lower and the air speed is higher than during other phases of flight, these surface coolers are typically overdesigned and add additional drag to the propulsion system, therefore increasing the engine specific fuel consumption (SFC). In addition, heat transfer fluids may be used to dissipate heat from generators within the aviation engine that produce electricity. In these instances, fluid cooling may be desired during any envelope of flight (cruise, ground idle, top of climb, etc.) and based on load and heat exchange requirements.
It would therefore be desirable to provide a robust method and apparatus for maintaining sufficient cooling to a heat transfer fluid, such as oil, passing through a heat exchanger apparatus during high temperature conditions for an aviation engine, yet without adding additional drag to the propulsion system during low temperature conditions. It is also desirable to provide a robust method and apparatus for maintaining sufficient cooling to a heat transfer fluid, such as oil, passing through a heat exchanger apparatus during increased load conditions. A heat exchanger apparatus that addresses the above issues is desired.